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A295045 Number of n X 2 0..1 arrays with each 1 horizontally or vertically adjacent to 0 or 2 1s. 4
3, 8, 19, 48, 120, 299, 747, 1865, 4656, 11625, 29024, 72464, 180921, 451705, 1127771, 2815704, 7029963, 17551696, 43821288, 109408531, 273160083, 681998289, 1702743904, 4251237649, 10614057408, 26500098080, 66162747313, 165188412465 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 2 of A295051.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = 2*a(n-1) + a(n-2) + a(n-3) - a(n-4).

Empirical g.f.: x*(3 + 2*x - x^3) / (1 - 2*x - x^2 - x^3 + x^4). - Colin Barker, Feb 21 2018

EXAMPLE

Some solutions for n=7:

..0..0. .0..1. .0..0. .1..0. .0..1. .1..0. .0..0. .0..1. .1..0. .0..0

..1..0. .1..0. .0..1. .0..0. .0..0. .0..0. .1..0. .0..0. .0..0. .1..0

..0..0. .0..1. .0..0. .0..0. .0..0. .0..1. .0..1. .1..1. .0..0. .0..1

..1..0. .0..0. .0..1. .0..0. .1..0. .0..0. .0..0. .1..1. .0..1. .0..0

..0..1. .1..0. .0..0. .1..0. .0..1. .0..0. .1..0. .0..0. .0..0. .1..0

..1..0. .0..0. .0..0. .0..1. .0..0. .0..0. .0..1. .1..0. .1..0. .0..0

..0..1. .1..0. .0..1. .1..0. .1..0. .1..0. .1..0. .0..1. .0..1. .0..0

CROSSREFS

Cf. A295051.

Sequence in context: A121811 A244208 A296329 * A181849 A164586 A018032

Adjacent sequences:  A295042 A295043 A295044 * A295046 A295047 A295048

KEYWORD

nonn

AUTHOR

R. H. Hardin, Nov 13 2017

STATUS

approved

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Last modified July 12 10:20 EDT 2020. Contains 335657 sequences. (Running on oeis4.)